1. Field of the Invention
This invention relates to drive devices for moving a lens, diaphragm, etc. in the photographic lens and, more particularly, to drive control devices suited to operate this lens, diaphragm, etc. with selection of the manual and motor-driven modes.
2. Description of the Related Art
The conventional circuit for selectively operating the manual and motor-driven modes of the apparatus of this kind has been constructed in the form as shown in FIG. 4. That is, a motor-drive/manual changeover signal coming through a signal line 8 enters an amplifier 12 and goes therefrom to a relay 14, thereby opening or closing a contact point 14a of the relay 14. Thus, changing over between these modes becomes possible.
Describing it in more detail, when the operator chooses the manual mode, the motor-drive/manual changeover signal functions, with the help of the amplifier 12, to set the relay 14 to the open state, so that the motor 5 is cut off from the supply of the motor-drive command signal from another signal line 1 through another amplifier 2. By this, direct driving of the lens by hand becomes possible. Meanwhile, in the motor-driven mode, the motor-drive/manual changeover signal coming through the amplifier 12 closes the contact point of the relay 14 so that the motor 5 and the amplifier 2 are connected to each other. Responsive to the motor-drive command signal, the motor 5 is driven to move the lens.
However, the above-described conventional example, because of its using the method of changing over between the motor-driven and manual modes by opening or closing the contacts of the relay 14, has the following problems:
1) Owing to the relay operation, consumption of electrical energy in an electric power source 13 becomes large. For the electric power source of the lens of the portable camera for home use, batteries are used in many cases. However, the increase of electric current consumption by the relay operation shortens the photographic time. This may cause a precious shutter opportunity to be lost.
2) Because of the contact operation, reliability is low and cost is high. In general, the relay contacts have an endurance span. After a certain time of use, therefore, the relay must be exchanged by a fresh one. The maintenance of this sort is very troublesome, too.